1. Field of the Invention
This invention relates generally to thin film magnetic transducers and more particularly to the magnetic yoke structures of such thin film transducers.
2. DESCRIPTION OF THE RELATED ART
A typical thin film prior art transducer is depicted in FIG. 1 herein. U.S. Pat. No. 4,295,173, Romankiw et. al, describes such a transducer in detail. The practice in the prior art in achieving resolution enhancement has been to provide thin pole pieces 5a and 7a at the front gap FG or read/write gap, while preventing saturation of the yoke by increasing the cross sectional area of the yoke away from the pole pieces, as in the legs 5 and 7. In reference to FIG. 1, thin film magnetic transducers are conventionally fabricated upon a substrate 1 which upon completion of fabrication has an end face adjacent a media M. The endface functions as a slider and rides on the air bearing, that is, the thin film of air between the slider and the disk surface. The magnetic transducer is fabricated as a thin film structure on the substrate 1 and comprises a magnetic yoke structure having legs 5 and 7. The thin film legs 5 and 7 are joined at the back gap BG. The other ends of the thin film legs 5 and 7, which are the pole pieces 5a and 7a, are of reduced thickness and lesser cross section and are closely spaced to define a front gap FG having a throat measured between the points x and y. The ends of the front gap pole pieces 5a, 7a confront the media M. The thin film legs 5 and 7, in the region between the back gap BG and the front gap FG are spaced apart, and one or more planar coils 8, having coil turns 8a are imbedded in an electrically insulating material between these portions of the legs. Passing electrical current through these coils induces a magnetic flux within the yoke. The front gap FG has a throat, the dimension of which extends between the points x and y, the point y being the end of the throat adjacent the media.
This design has been effective for low coercivity media. As linear bit densities increase, higher coercivity media is required. Concomitantly, a thin film inductive transducer must be capable of generating a write field of sufficient magnitude to overwrite the previously written data, so that there are no residual signals from the overwritten data to interfere with the ability to properly read-back the newly written signal, with respect to both the amplitude and phase of that new signal.
The practice of the prior art, to avoid saturation of the yoke structure in a thin film head, has been to increase the cross-sectional area of the yoke structure, especially the legs, in regions away from the pole tips. However, this has not been effective in preventing saturation of the pole structure when fields of high flux density are needed for writing on high coercivity media, especially if the throat height, that is, the dimension between the points x and y, as seen in FIG. 1, is long. Leakage flux, between the confronting faces of the yoke structure along the throat and across the poles in regions 5c and 7c of FIG. 2, significantly reduces the flux density at the tips of the yoke structure adjacent the media, which is undesirable.
Saturation phenomena, in structures of the type of FIG. 1, is discussed by Keloy and Valstyn, IEEE Transactions On Magnetics, V. Mag-16, # 5, Sept. 1980, pg. 788-790. Saturation has been experienced in practical applications of the prior art, when writing on high coercivity media, where it has been necessary to increase write currents in order to provide flux density at the media sufficient to record well written transitions. Specifically, as higher magnetic fields are required to cause saturation reversal in the media, for recording magnetic transitions, magnetic field densities in the yoke structure of a transducer, having legs and other parts of a given cross sectional area, increases. At some point, these magnetic field densities become large enough to saturate sections of the yoke structures in the regions where the transition is made between the thin film pole pieces, such as 5a and 7a, and the thicker yoke area, such as legs 5 and 7. In this connection, refer to FIG. 2. In FIG. 2, a typical flux path is indicated in a fragmentary portion of the yoke structure, particularly in the regions adjacent the upper end of the throat x,y of the front gap FG. In FIG. 2, the arrows outline the legs 5 and 7, which are not shown, of the yoke structure. The arrow length is generally proportional to the magnitude of magnetization. The arrows approximately indicate the magnetization distribution in gap regions of the head in FIG. 1. Regions of magnetic saturation are illustrated at 5c and 7b. If there is no saturation in the back gap BG and in the legs in other regions than those indicated adjacent the front gap FG, (poles tapered in z direction), the region 7d saturates first, and the regions 5c and 7c saturate as write current is increased.
Thus the structure of FIG. 1, while effective in writing in low coercivity applications, experiences complex magnetic saturation patterns in the yoke structure, at least adjacent the upper end of the throat of the front gap F,G which interferes with the development, or production, of magnetic flux of sufficient intensity, linking a high coercivity medium M, to provide effective writing, or over writing, in the magnetic layer on the media.